The Popular Mobilization Forces (PMF) is an Iraqi state security service that Iran has infiltrated and uses to wield significant influence in Iraq. Iran’s cooptation of the PMF enables Tehran to pursue its objectives in Iraq while obfuscating its actual involvement in Iraqi internal affairs. Understanding how Iranian leaders wield direct and indirect influence over this significant component of the Iraqi security sector is crucial as the United States considers how to deter Iranian-backed Iraqi militias from attacking US forces in Iraq and Syria.